1. Field of the Invention
The present invention relates to a hybrid car having an internal combustion engine and an electric motor as driving sources and a driving apparatus therefor. The present invention also relates to a hybrid type four-wheel-drive car having a transmission with a clutch and a control apparatus therefor.
2. Description of the Related Art
Examples of hybrid cars having an internal combustion engine and an electric motor as driving sources are known from Japanese Patent Laid-open Nos. 2000-272367 and 2001-63392. Disclosed in Japanese Patent Laid-open No. 2000-272367 is a four-wheel driving apparatus, in which a generator is driven by an engine driving a front wheel and an electric power generated by the generator is used to drive an electric motor driving a rear wheel (refer, for example, to page 3 and FIG. 1 of Japanese Patent Laid-open No. 2000-272367). In Japanese Patent Laid-open No. 2001-63392, a front-and-rear wheel drive vehicle is disclosed, in which an engine driving a front wheel drives a generator, while a motor generator driving a rear wheel is driven by an electric power generated by a generator and supplied by way of an inverter or an electric power accumulated in a capacitor (refer, for example, to page 3 and FIG. 1 of Japanese Patent Laid-open No. 2001-63392).
A hybrid four-wheel-drive car having an engine for driving either pair of front or rear wheels and a motor for driving the other pair of wheels, either front or rear, is disclosed, for example, in Japanese Patent Laid-open Nos. 2002-218605 and Hei 8-300965 and in the November issue (No. 578) of “Nikkei Mechanical” (pp. 53 to 58). An automatic manual transmission for a parallel type hybrid car is disclosed, for example, in Japanese Patent Laid-open No. 2000-272360.
Disclosed in Japanese Patent Laid-open No. 2002-218605 among other prior art techniques is a control apparatus of a driving force for a vehicle provided with an internal combustion engine driving at least either pair of front or rear driving wheels and a generator driven by the power from the internal combustion engine. This driving force control apparatus for a vehicle is provided with driving wheel slip estimation means that estimates whether or not the driving wheels slip during acceleration. The control apparatus is further provided with generator control means that is activated when the driving wheel slip estimation means estimates that the driving wheels slip in acceleration and controls so as to bring torque of the generator to a level equivalent to a power generating load torque corresponding to the amount of acceleration slip the driving wheels make.
Disclosed in Japanese Patent Laid-open No. Hei 8-300965 is a front-and-rear wheel drive vehicle having an engine for driving either pair of front or rear wheels and an electric motor for driving the other pair of wheels, either front or rear. This front-and-rear wheel drive vehicle is provided with means for detecting the value of μ on a road surface. The vehicle is further provided with control means that operates the electric motor so as to bring an output torque of the electric motor to a predetermined value corresponding to the detected value of μ when the vehicle is started with the detected value of μ being a predetermined value or less.
In an electric motor-driven four-wheel-drive vehicle, in which the electric motor is driven directly by an output from a generator (hereinafter referred to as the “motor-driven four-wheel-drive vehicle”), the following control is provided. Specifically, when, for example, an attempt is made to start a vehicle or get the vehicle out of a rut, in which case there is a great torque requirement with a low vehicle speed, a current value and a voltage value of a power output from the generator are controlled so that a large current value and a small voltage value of a power input to the electric motor are provided. While the vehicle is running, in which case there is a small torque demand with a high vehicle speed, on the other hand, the current value and the voltage value of the power output from the generator are controlled so that the small current value and the large voltage value of the power input to the electric motor are provided. That is, the motor-driven four-wheel-drive vehicle is controlled so that the maximum torque is output from the electric motor when the vehicle is started and the torque of the electric motor decreases as the vehicle speed increases.
According to such control as mentioned above, driving performance comparable with that offered by a mechanical type four-wheel-drive vehicle can be provided by the motor-driven four-wheel-drive vehicle over a wide operating range. There is, in the motor-driven four-wheel-drive vehicle, a need for improving vehicle running performance even further so as to bring it near that achieved in a mode in which two wheels are driven (hereinafter referred to as the two-wheel-drive mode).
In Japanese Patent Laid-open No. 2000-272360, an automatic clutch type transmission mounted in a two-wheel-drive parallel hybrid car is disclosed for improved fuel economy. It is, however, difficult to apply this clutch type transmission to a four-wheel-drive hybrid car having an engine for driving either pair of front or rear wheels and a motor for driving the other pair of wheels, either front or rear. Japanese Patent Laid-open Nos. 2002-218605 and Hei 8-300965 are not, on the other hand, concerned with disconnection of torque generated when the clutch is disengaged during a gearshift. Unless a driving force is obtained during a gearshift, there is likelihood that acceleration performance will be degraded during a gearshift, performance in getting the vehicle out of mud will be degraded, and other performance degradation will result.
To solve these problems, it will readily occur to those skilled in the art that, in the hybrid car using the clutch type transmission, a battery or a capacitor mounted therein is used during a gearshift to apply an electric power to the motor when the clutch is disengaged, thereby obtaining a driving force. Simply detecting a disengaged condition of the clutch and letting the motor generate torque could give a driver an awkward feeling that does not exactly match his or her intention. There is still another problem that the battery and capacitor are expensive. There is therefore a need for obtaining the driving force using a simpler and easier method.